King's College London

Objective: It has been debated whether different stages in the human sleep cycle preferentially mediate the consolidation of explicit and implicit memories, or whether all of the stages in succession are necessary for optimal consolidation. Here we investigated whether the selective deprivation of slow wave sleep (SWS) or rapid eye movement (REM) sleep over an entire night would have a specific effect on consolidation in explicit and implicit memory tasks.
Method: Participants completed a set of explicit and implicit memory tasks at night, prior to sleep. They had one control night of undisturbed sleep and two experimental nights, during which either SWS or REM sleep was selectively deprived across the entire night (sleep conditions counterbalanced across participants). Polysomnography recordings quantified precisely the amount of SWS and REM sleep that occurred during each of the sleep conditions, and spindle counts were recorded. In the morning, participants completed the experimental tasks in the same sequence as the night before.
Results: SWS deprivation disrupted the consolidation of explicit memories for visuospatial information (η2p =.23), and both SWS (η2p = .53) and REM sleep (η2p = .52) deprivation adversely affected explicit verbal recall. Neither SWS nor REM sleep deprivation affected aspects of short-term or working memory, and did not affect measures of verbal implicit memory. Spindle counts did not correlate significantly with memory performance.
Conclusions: These findings demonstrate the importance of measuring the sleep cycles throughout the entire night, and the contribution of both SWS and REM sleep to memory consolidation.